Regal 215 tenor guitar scale length issue

[tom brahan]

My first post. I picked up Regal 215 knowing that cracked bridge had to be replaced. When I started to measure for new bridge placement, I ran into problem. The old bridge has uncompensated straight saddle set at an almost perfect 23 inch scale length, but when I double checked the 12th fret measurement it is an almost perfect 11 3/8 inch. This would make a
22 3/4 inch scale, which not an uncommon tenor scale. The 4th thru about 10th frets seem to be ever so slightly closer to each other than fret charts indicate for a 22 3/4 scale and all frets are short of a 23 inch scale. Fretboard and frets look original. Never had chance to hear it strung, so I don't know about intonation. Should I just set the new bridge to match old one? Did Regal set these up like this to correct intonation? Should I make compensated bridge and saddle and replace fretboard with standard 23 inch scale spacing? When I get through, Id like it to play in tune up the neck.

[Greg Robinson]

Hi Tom, and welcome to the new MIMForum!

It sounds like your Regal had the frets laid out using the old "rule of eighteen". This was common practice on older instruments, as dividing a scale length by 18 is a lot easier than using the more correct "12th root of 2". This is calculated as follows:
SL-(SL/(2^(N/12)))=D
Where:
SL is scale length
N is fret number
D is the distance of that fret from the nut.


The rule of 18 places the frets progressively short of the more "correct" position.
Also, because the rule of 18 does not calculate each fret position individually, but relys on the previously calculated value, there are compounding rounding errors.

But, this isn't all bad. Because the rule of 18 places the frets short of their "correct" positions, it includes some built-in compensation. It usually works out that with the saddle placed at the scale length it's been calculated from, results in reasonable intonation.

Either way, a 23" scale calculated with the rule of 18, or a 22-3/4" scale with 1/4" compensation, sounds reasonable for your instrument. You can always rig up some sort of tailpiece and temporary bridge/saddle to confirm or adjust for intonation before committing to gluing it down.

Good luck!

[Mark Swanson]

That's good Greg!
You can also make a temporary tailpiece that will hold the strings so you can move the bridge around to find the sweet spot.

[tom brahan]

thanks. I never heard of that, but it makes sense and fits my observations.

[tom brahan]

Thanks for advice. I took a little time off for a couple quick by-passes. Now it looks like I'll have a lot of time to plan before I get back to this tenor.
Now it looks like the fretboard is too far gone to be refretted. Wood is so soaked with oil, dirt, etc., that the frets just pull out with no effort. Just rotten down deep in the board. So, I'll be replacing the fretboard. This gives me the chance to cut the frets however I want to get the best intonation. What's the best way to back-figure the fret position scale length assuming a saddle centered at 23". I find a lot of info on suggested saddle set back and compensation for six-string, but next to nothing for four-string. Lot's of info for standard guitar scale lengths, but almost nothing for short, tenor scale.